An automobile radiator, air conditioner, intercooler, oil cooler, or other heat exchanger is assembled by brazing together a working fluid passage material comprised of an Al—Cu-based alloy, Al—Mn-based alloy, Al—Mn—Cu-based alloy, etc. and fins comprised of an Al—Mn-based alloy etc. The fin material is required to have a sacrificial anodization effect in order to prevent corrosion of the working fluid passage material and is required to have an excellent sag resistance and erosion resistance in order to prevent deformation or erosion of the brazing material due to the high temperature heating at the time of brazing.
JIS 3003, JIS 3203, and other Al—Mn-based aluminum alloys are used as fin materials because Mn effectively acts to prevent deformation or erosion of the brazing material at the time of brazing. An Al—Mn-based alloy fin material may be given a sacrificial anodization effect by the method of adding Zn, Sn, In, etc. to this alloy to make it electrochemically anodic (Japanese Patent Publication (A) No. 62-120455) etc. To further improve the high temperature buckling resistance (sag resistance), there is the method of introducing Cr, Ti, Zr, etc. into the Al—Mn-based alloy (Japanese Patent Publication (A) No. 50-118919) etc.
However, recently, heat exchangers are increasingly being required to be made lighter in weight and lower in cost. The working fluid passage material, fin material, and other heat exchanger materials are increasingly being required to be made thinner. However, if for example making the fins thinner, the heat conduction sectional area becomes smaller, so the heat exchange performance falls and final product heat exchanger has problems in strength and durability. Therefore, a much higher heat conduction performance, strength after brazing, sag resistance, erosion resistance, and self corrosion resistance are desirable.
In conventional Al—Mn-based alloys, the Mn dissolves into the matrix due to the heat at the time of brazing, so there is the problem that the thermal conductivity falls. As a material for solving this difficulty, an aluminum alloy limiting the Mn content to not more than 0.8 wt % and containing Zr: 0.02 to 0.2 wt % and Si: 0.1 to 0.8 wt % has been proposed (Japanese Patent Publication (B2) No. 63-23260). This alloy has an improved thermal conductivity, but the amount of Mn is small, so the strength after brazing is insufficient and the fins easily collapse or deform during use as a heat exchanger. Further, the potential is not sufficiently anodic, so the sacrificial anodization effect is small.
On the other hand, by speeding up the cooling rate when casting an aluminum alloy melt into a slab, even if making the Si and Mn contents etc. 0.05 to 1.5 mass %, the intermetallic compounds crystallizing at the slab casting can be reduced in size to a maximum size of not more than 5 μm. It has been proposed to improve the fatigue properties of the fin material by rolling this slab (Japanese Patent Publication (A) No. 2001-226730). However, this invention has as its object the improvement of the fatigue life. While it describes making the cast slab thinner etc. as means for speeding up the cooling rate when casting the slab, no specific disclosure such as thin slab continuous casting by a twin-belt casting machine in industrial scale operations can be found.